Herein are described flexible electrostatographic imaging members including electrophotographic imaging members, such as photosensitive members, or photoconductors, or photoreceptors, and ionographic imaging members useful in electrostatographic apparatuses which, for example, include printers, copiers, other reproductive devices, and digital apparatuses.
Since typical flexible electrostatographic imaging members do exhibit upward curling after application of the top layer, an anti-curl back coating is required, in embodiments, to be coated at the back side of the members to render flatness. Flexible imaging members may include seamed or seamless belts or sheets in scroll form or belts mounted over a rigid drum (a drelt). Under electrostatographic imaging function conditions, a flexible imaging member belt dynamically cycling over a belt support module has been seen to encounter a gradual increase in belt drive torque caused by static built-up in the anti-curl back coating as a result of its mechanical interaction against the belt module support rollers and backer bars. Static built-up can exacerbate anti-curl back coating wear, which can create debris and dusty machine cavities. This, in turn, leads to contamination of copy printouts, and can also cause the imaging member belt to exhibit upward curling due to its thickness reduction. The final result is an anti-curl balancing result. Exhibition of imaging member upward curling affects surface charging uniformity, and thereby impacts copy printout quality. Moreover, excessive static built-up in the anti-curl coating during dynamic imaging member belt function has also caused the belt to stop rotating.
In an attempt to suppress or eliminate the static built-up problem, specific embodiments described herein include flexible photosensitive members comprising an anti-curl back coating having a conductive filler dispersed in a binder. In embodiments, the binder of the anti-curl back coating is a polymer and the conductive filler is lignin sulfonic acid doped polyaniline (Ligno-PANi). In embodiments, the undesirable characteristic of steep rise in conductivity of the anti-curl back coating, often time found to be associated with carbon black dispersion levels, can be avoided by using the Ligno-PANi filler. Process control, in embodiments, has thereby become more robust. In addition, in embodiments, build up of static charge during belt use in an electrostatographic imaging machine is reduced or eliminated. This, in turn, causes a reduction in anti-curl back coating wear, and thereby creates a debris and dust-free imaging member belt machine function condition. The notable drive torque is not increased, and belt stall is no longer an issue, in embodiments. Furthermore, reduction in anti-curl back coating wear maintains imaging member flatness for extended belt function assurance free of copy printout impact associated with the upward belt curling problem, in embodiments.
Flexible electrophotographic imaging members, including photoreceptors, photosensitive members, photoconductors, and the like, typically include a photoconductive layer formed on an electrically conductive flexible substrate or formed on layers between the flexible substrate and photoconductive layer. The imaging member does also include an anti-curl back coating applied to the back side of the flexible substrate to render imaging member flatness. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy receiving member, and fused thereto to form a copy or print.
The photoconductive layer may include a single layer or several layers. In embodiments wherein there are two layers, these two layers may include two electrically operative layers positioned on an electrically conductive layer with a photoconductive layer sandwiched between a contiguous charge transport layer and the conductive layer. The outer surface of the charge transport layer is normally charged in the dark with a uniform negative electrostatic charge, and the conductive layer is used as an electrode.
Since one or more layers are applied by, for example, solution coating to a flexible supporting substrate and each then subsequently dried at elevated temperatures, it has been found that the resulting photoconductive member tends to curl. This is due to the difference in thermal contraction of the substrate and the photoconductive layers, and also is due to the specific nature of the polymers used for each layer. Curling is undesirable for several reasons, including the fact that different segments of the imaging surface of the photoconductive member are located at different distances from charging devices, developer applicators, and the like, during the electrophotographic imaging process. Undesirably imaging member curling also prevents the receiving paper from making intimate contact with the imaging member surface for effectual toner image transfer. The result is that the quality of the ultimate developed images are adversely affected. For example, non-uniform charging distances can be manifested as variations in high background deposits during development of electrostatic latent images.
Coating may be applied to the back side of the supporting substrate opposite the photoconductive layer to counteract the tendency to curl. However, difficulties have been encountered with these anti-curl coatings. Anti-curl back coating will occasionally delaminate under normal function conditions of image belt cycling in copiers, duplicators, printers and facsimile machines. Anti-curl back coating delamination is caused by adhesion bond failure due to its excessive mechanical and frictional interactions against the components of the belt support module. Delamination is particularly troublesome in high-speed automatic copiers, duplicators and printers, which require extended cycling of the photoreceptor belt. Occurrence of delamination is very frequent under dynamic imaging member belt cycling conditions when severe static charge is built-up in the anti-curl back coating. Moreover, delamination is accelerated when the belts are cycled around small diameter rollers and rods.
Since the anti-curl back coating is an outermost exposed layer, it has further been found that during cycling of the photoconductive imaging member in electrophotographic imaging systems, the relatively rapid wearing away of the anti-curl coating also results in the curling of the photoconductive imaging member due to thickness reduction by wear. In some tests, the anti-curl back coating was completely worn off in about 150,000 to about 200,000 belt cycles. This erosion problem of anti-curl back coating is even more pronounced when photoconductive imaging members in the form of webs or belts are supported in part by stationary guide surfaces, e.g. backer bars. The anti-curl layer may wear away very rapidly and produce debris, which scatters and deposits on critical machine components such as lenses, corona charging devices, and the like. This, in turn, adversely affects machine performance. Moreover, the debris from bisphenol A type polycarbonate anti-curl backing layers tends to deposit on backer bars and other support members. These deposits result in a loud high pitched humming sound emitted during image cycling.
It has also been observed that when conventional belt photoreceptors using a bisphenol A polycarbonate anti-curl backing layer are extensively cycled in precision electrostatographic imaging machines, undesirable defect print marks were formed on copies.
It has been found that certain polycarbonate film forming polymer binders containing a monomeric unit derived from 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane reduced or eliminated the above problems. In addition, inorganic metal oxides and silica fillers or organic PTFE and lubricant stearate fillers incorporated into the material matrix of anti-curl back coating, have also been proven to be effective in imparting wear resistance enhancement.
However, there still remains a problem in that the photoreceptor belt can build up static charge on the insulating anti-curl backing coating (ACBC) of the belt as it is moved over the rollers. Static built-up can cause several of problems. In the film industry, the resistivity range of from about 10−6 to about 10−14 ohms/sq, or from about 108 to about 1013 ohms/sq, is referred to as the static dissipative range, which means not resistive enough to build up static charge, but not really conductive. It is desired to be able to modify the resistivity of the coating into this desired range. It is further desired to prevent build up of debris and dusty machine cavities, which, in turn, can lead to contamination of copy printouts, can cause the imaging member belt to exhibit upward curling due to its thickness reduction, and can result in an imbalance, and finally, to belt stall. It is further desired to prevent the belt from premature cracking.